In recent years, a wireless train control system has been attracting attention. Specifically, wireless communication is performed between a wireless base station installed along a railroad track and a train (between the ground and a car), and the operation and speed of the train are controlled on the basis of information transmitted through the wireless communication. The wireless train control system is advantageous in terms of introduction and maintenance costs because it does not require a track circuit, as compared with a conventional train control system based on a fixed block section. Since the block section can be flexibly constructed without being limited to the fixed section, the density of train operation can be increased. Therefore, the wireless train control system is also advantageous in terms of operational costs.
In the wireless train control system, the industry science medical (ISM) bands which do not require a license are often used for the wireless communication between the ground and a car. However, the ISM bands are widely used in other communication systems such as a wireless local area network (LAN) conforming to the IEEE 802.11 standard and Bluetooth (registered trademark), and instruments for these other communication systems located in a train or a railroad building may be a major source of interference for the wireless communication of the wireless train control system. In the wireless train control system, interference resistance of a wireless communication device is an important factor for the stable wireless communication between the ground and a car.
A method for use in a multicarrier transmission system such as orthogonal frequency division multiplexing (OFDM) has been proposed as a technique for increasing the interference resistance performance of a wireless communication device and achieving high-quality communication (Patent Literature 1). Specifically, on the transmission side, null symbols are distributed within a time frame defined by a frequency axis and a time axis by using an arrangement pattern stored in a memory. On the reception side, the interference power is measured at each of the positions of the null symbols within the time frame, whereby a highly accurate interference power value is acquired, and the acquired interference power value is used for a transmission control process and a synthesis process between antennas.